Systems and methods for power generation utilizing combustion of carbonaceous or hydrocarbon fuel(s) with carbon dioxide as a working fluid are described in U.S. Pat. No. 8,596,075 to Allam et al., which is incorporated herein by reference. Such systems and methods utilize a high-pressure recuperative Brayton system with CO2 as a working fluid wherein substantially pure oxygen is used for the combustion of fuel at high pressures (e.g., approximately 200 bar to 400 bar) and high temperatures (e.g., about 600° C. to about 1,600° C.). In some examples, the fuel may be natural gas (i.e., a hydrocarbon gas mixture consisting primarily of methane), and/or a fuel derived from the partial oxidation of coal, biomass and/or residual petroleum refining products such as, for example, heavy residual oil fractions or petroleum coke. The combustion product stream at such pressures and temperatures is expanded across a turbine with an outlet pressure of about 20 bar to about 40 bar. The expanded stream can then be cooled (e.g., with a recuperative heat exchanger) and treated for removal of water or other impurities to provide a substantially pure stream of CO2, which can be compressed and reheated (e.g., against the turbine outlet stream in the recuperative heat exchanger) before being recycled into the combustor. Optionally, part or all of the CO2 may be withdrawn for sequestration and/or secondary uses, such as enhanced oil recovery, as described in U.S. Pat. No. 8,869,889 to Palmer et al., the disclosure of which is incorporated herein by reference. Such power cycles can provide high efficiency power production with capture of substantially produced CO2. For example, such power production cycle combusting natural gas to provide a turbine inlet stream at a pressure of 300 bar and a temperature of 1,150° C. and a turbine outlet stream at a pressure of 30 bar can exhibit a net efficiency (on a lower heating value basis) of about 59% with complete carbon capture. This high efficiency is achieved in part by introducing a second heat input at a temperature level below about 400° C. to compensate for the large difference between the specific heat of CO2 at lower temperatures at the high and low pressure used in the system.
A key requirement for such power cycles is large quantities of substantially pure, highly pressurized gaseous oxygen. A 300 MW power production plant working under conditions as discussed above typically requires about 3,500 metric tons per day (MT/D) of oxygen at 99.5% purity and 30 bar minimum pressure produced from a cryogenic air separation plant. The inclusion of an oxygen plant significantly increases the capital cost of a power production system operating as described above and also consumes a large quantity of power during operation of the power production cycle. As noted above, such systems and methods have been shown to provide increased efficiency through addition of heat that is not recuperated from the combustion product stream. In some embodiments, the added heat may be derived from adiabatic heat produced by compressors that increase the pressure of an inlet air stream in a cryogenic oxygen production process and additionally heat derived from at least part of the CO2 recycle compression. Nevertheless, there still remains a need in the art for further power production cycles that can achieve high efficiency with substantially complete carbon capture and can be implement with reduced capital expenditures and operating costs.